Jared Harris is a charmer, not that you'd know that by watching any of his films. The red-headed actor with the startlingly intense eyes was raised in the business: his father, Richard Harris, was King Arthur in Camelot and his mother, a Welsh beauty, would go on to marry Rex Harrison. Jared has played a jail's worth of villains and a classroom's worth of brainiacs—the right preparation to tackle the role of Sherlock Holmes' smartest opponent, Moriarty. With his entrance, Holmes is in real peril—and audiences can't wait to see Harris go mind-to-mind with the genius detective.

I've read that Arthur Conan Doyle invented Moriarty just to find a way to kill off Sherlock Holmes because he was sick of writing the stories. He wanted to make the ultimate villain.

Well, it was not the only reason. I mean, that wasn't the reason why he invented Moriarty. The reason that Conan Doyle invents Moriarty is that he has a super sleuth who can solve any problem. So it's a bit like Superman, you know? There's no real opposition to Superman so you have to invent kryptonite. So I guess Moriarty is like Sherlock Holmes' kryptonite. He invents this character who's as smart, as sharp, as intelligent, as devious and as manipulative, but lacks whatever moral restraints that Sherlock Holmes has so that he's a very very dangerous opponent. That was the idea behind creating him. And then, he only appears in two stories himself. The rest of the time, he's talked about. But certainly in The Final Problem, at that point, Conan Doyle was fed up with writing Sherlock Holmes stories and wanted to finish it so then he did the natural thing and brought the two forces together. But then not long after that, I think there was such an outcry for more Sherlock Holmes and I'm sure they wafted great big fat sterling notes under his nose and he changed his mind and brought him back.

That's pretty hard to resist, those big fat Sterling notes.

Well, they were huge back then as well, those old five-pound notes. They were great big white things that were like small letters. They were quite significant back then.

It seems like it'd be hard to pickpocket money back then if money was so big.

You'd hear amazing things about what they could get up to back then, but yeah, they probably just whacked you over the head and picked your wallet.

So if you're playing the one guy who might be even smarter than Sherlock Holmes, is your type of intelligence different than the way Downey plays his intelligence?

Obviously, otherwise I'd just end up being a bad version of Robert, which, you know, I can't copy what he does—he's unique, you know. That's something that we talked about a lot. Within a limited amount of screen time, how do you convey the idea? Sherlock Holmes goes a long way towards creating the impression you're trying to create for you, which is great, because of the respect he gives the character and the way he talks about him—and generally, anything that Sherlock Holmes says, one takes as being gospel. And then, for me I think the character, he's like a grandmaster chess player—they're always thinking 12 or 14 moves ahead. You always want to have a sense that there's more to the plan to be unfolded. And then the other thing you always see in movies with bad guys is that they all say too much. They all give everything away. And so I didn't want to say anything unless I absolutely had to. What happens in these things is that the bad guy becomes a vehicle for the plot. So every time he opens his mouth, exposition falls out like a sewer. With villains it's a little bit like watching a stripper—no offense—but the second they take their clothes off, you lose interest. As soon as you know what the villain is up to, your interest in that character starts to dwindle. So the longer you can put off the moment of revelation about what the person is up to, you maintain that tension with the audience.

Is Moriarty like the Joker, just this source of anarchy?

That character I think was trying to prove a point about human nature with the Batman. In this, Moriarty's manipulating what he understands about human nature, but he's got his own purpose. He isn't trying to prove some sort of existential point. In fact, my impression was that by and large, until Sherlock Holmes dropped into his storyline, he's largely not concerned with him. He's pursuing this agenda that's irrespective of what Sherlock Holmes was up to and then eventually, he can't ignore it any longer. But he isn't out from the beginning to make some point to him, which is my impression of the Joker.

Do you get to use his amazing air rifle?

Ah! I just don't know how much one can give away! That element is in the story, but I can't say who employs it.

Are you worried about annoying the purists?

It sounds odd, because I'm sure the Sherlock Holmes purists will just throw eggs in my face for even saying this, but they really are sincere about remaining true to the spirit of Conan Doyle's work. And whenever they can and could mine from the combined works that was going to be useful in the story, they did. So, I mean even some of the lines of dialogue pop up. But you know, I think what happens in Sherlock Holmes is that there was a tradition that sprung up from the time when it first started to be represented on film, which mirrors the Victorian ideal about the time period: this sort of genteel, well dressed, well appointed period that these people lived in, which has come down from Basil Rathbone and Jeremy Brett and everything about the BBC version. But I think if they actually went back to Victorian England—I mean, certainly the way that Charles Dickens wrote about it—it was an absolute slum. Some of the people were living well-off, but most of the people were living in these f--king hell holes. And I imagine that it's a lot closer to Guy Ritchie's version in terms of the environment that these people were in. And I think with Robert Downey Jr's Sherlock, he's taken the darker elements of Sherlock Holmes, which are absolutely there in Conan Doyle's writing, and he's brought those up to the forefront rather than sweeping them under the carpet.

I was wondering: You've played a lot of villains, and you've played a lot of doctors. Is there any connection between doctors and villains?

When one has had one's healthcare benefits disapproved, I suppose yes. You're villain-bound. I was useless in science, so it can't be anything innate. Probably it's the fact that I'm, generally speaking, because of Mad Men cleanly shaved and my hair's all neat and tidy, so I've got that kind of professional look.

Does that mean you couldn't play a hippie if you wanted to?

You'd have to make a wig, so it depends on whether they want to spend that money on you or not.

So, there's the other Moriarty right now, which is Andrew Scott on the BBC. Have you avoided watching his version?

I saw it last year, but I haven't talked to him. I mean, it's so different in terms of the things we were required to do, because it's updated. The whole way of behaving is modern and casual—he was a sort of slinky villain, you know? But I enjoyed it. I thought Benedict [Cumberbach, who plays Sherlock] was a fantastic actor. I thought they did a good job with it. It's got all those things about Sherlock Holmes that you like. But I really didn't see that many of them. I think I saw one on the plane going over before I started the job.

And before you even started the job, the first Sherlock movie from 2009 had the voice of Moriarty at the end. Obviously, that wasn't you, but was there any temptation to continue to sound like him?

No. There was all that crazy stuff about that voice being Brad Pitt or something, which I'm sure came about because Guy and Brad have worked together in Snatch. But it wasn't, not at all. I will not say who it was, but I know who it was. That would just get me into big trouble.

Is it possible that Moriarty is misunderstood?

Oh god, no. [Laughs] Again one of the things that they did not do, which is provide some bulls--t explanation as to why this person did what he did—he was abused as a child or some bulls--t like that. I'm with William Golding [author of Lord of the Flies] on that one. He said that the more you explain a character, the more you diminish him, and I agree. The lesser you know, the better. It was the same mistake with Hannibal Lector. As soon as you found out that he'd been imprisoned as a child in World War II and forced to eat his sister, all the mystery went out of the character.

Did you have a favorite set piece?

I don't have a favorite set piece necessarily, but one of the things that is fantastic about doing that film and doing movies in general on that scale is that you get to go to places where you would normally as a tourist only get to see in passing. We went to these amazing estates around, outside of London, National Trust castles and then you get given a little tour. They take you around and show you all these places, the history there—it's stunning. That part is one of the great perks of this job. We went to the palace that Elizabeth I, before she was queen, she maintained her residence and they pointed out the tree that she was in sitting in when they told her her sister had died and she was going to be queen of England. It's just fantastic to be able to walk around and see all that stuff.

Wow, it's very convenient for her to be sitting somewhere outside and pretty instead of just in one of the boring rooms.

So it could rather have been made up, you think? That's what you're saying? You're casting aspersions on it?

I'm just saying, if I was queen, I'd always hang out and be seen in scenic places-

In a tree? Waiting just to be told.

You might as well have your legacy be as romantic as possible.

I would've been sitting outside as much as possible, too, because then you'd see the people with swords come after you and you could run in the other direction. They'd try to chop each other's heads off all the time back then. Sitting in a little room makes you very easy to trap.

Exactly.

It was very dangerous job being related to royalty back then. It was a short life expectancy.

It's true. You shouldn't even marry into it. You'd just get your head cut off in a second.

Back then. It's a bit different. It's not quite what it used to be. Most of them are broke. You have to support them.

So now that you're about to play a villain in a very big movie, does that mean that you can walk down the street and scare children?

I don't have the beard, so I'll probably go unrecognized, which is what I like. I like being able to walk around in disguise as myself. I don't know. I remember watching John Lithgow on a talk show after a movie called Ricochet, I think, had come out. He played a really crazy nutball psychopath villain and he's just going to visit some friends in their apartment building and he calls the lift, and the lift door opens, and the woman sort of looks up and is about to step out, and sees John and makes eye contact with him, and he smiles at her and she screams in terror and presses the ‘close' button and tries to get away from him. I haven't had that experience yet, but I'll let you know when I do.

You should. That's raw power.

That means you've done your job. I won't need a Halloween costume. I'll just go as myself and scare people.